Process for manufacturing an oxirane

ABSTRACT

Process for manufacturing an oxirane by reaction between an olefin and a peroxide compound in a reactor containing a liquid phase, in the presence of water, one or more organic solvents, a catalyst and one or more compounds for increasing the selectivity of the catalyst toward epoxidation reactions, in which: if the process is performed in batchwise mode, the liquid phase present in the reactor when the reaction starts, if the process is performed continuously, all of the liquid phases that are fed continuously into the reactor has/have a total organic solvent content of at least 0.1 g/kg and of not more than 675 g/kg.

The invention relates to a process for manufacturing an oxirane byreaction between an olefin and a peroxide compound in the presence of azeolite-based catalyst. The invention relates more particularly to aprocess for manufacturing 1,2-epoxypropane (or propylene oxide) byreaction between propylene and hydrogen peroxide, and to a process formanufacturing 1,2-epoxy-3-chloropropane (or epichlorohydrin) by reactionbetween allyl chloride and hydrogen peroxide.

It is known practice to manufacture propylene oxide by epoxidation ofpropylene using hydrogen peroxide in the presence of a catalyst of TS-1type, as described, for example, in patent application EP 0 230 949.This known process has the drawback of leading, under certainconditions, to low selectivities and to a deactivation of the catalyst.

It is also known practice to add to the reaction medium variousadditives that interact with the acidic sites of the catalyst and, in sodoing, make it possible to increase the selectivity thereof towardepoxidation reactions. Thus, patent applications EP 0 712 852 and EP 0757 043 describe for this reaction the use of a metal salt, but suchadditions generally result in a reduction in the activity, and, what ismore, the reaction conditions used make it necessary periodically orvery frequently to regenerate the catalyst, following its deactivation.

The invention is directed toward overcoming this drawback by providing aprocess for manufacturing an oxirane that shows both a high selectivityand a high conversion, as well as a minimum deactivation of thecatalyst.

The invention consequently relates to a process for manufacturing anoxirane by reaction between an olefin and a peroxide compound in areactor containing a liquid phase, in the presence of water, one or moreorganic solvents, a catalyst and one or more compounds for increasingthe selectivity of the catalyst toward epoxidation reactions, in which:

-   if the process is performed in batchwise mode, the liquid phase    present in the reactor when the reaction starts-   if the process is performed continuously, all of the liquid phases    that are fed continuously into the reactor has/have a total organic    solvent content of at least 0.1 g/kg and of not more than 675 g/kg.

The invention is based on the surprising observation that, in thepresence of an organic solvent content that is lower than thosegenerally recommended, both a high selectivity and a high conversionrate (activity) are obtained. Thus, according to the invention, it isimportant that, in the case of a batchwise process, it is the liquidphase present in the reactor during the start of the reaction thatsatisfies this condition, whereas, in the case of a continuous process,it is the liquid phase fed continuously into the reactor that satisfiesit. It should be noted in this respect that this liquid phase may be fedin one or more flows into the reactor and that, in the latter case, itis the total organic solvent content relative to all of the liquids fedinto the reactor that is concerned.

In the text hereinbelow, the expression “reaction medium” is intended todenote the liquid phase present in the reactor and containing theolefin, the peroxide compound, the water, the organic solvent(s), thecompound(s) for increasing the selectivity of the catalyst, the oxiraneformed and dissolved, and any by-products.

One of the essential characteristics of the invention lies in theaddition, to the liquid phase in which the reaction proceeds, of acompound for effectively limiting the side reactions that give rise tothe formation of undesired by-products, and thus for increasing theselectivity of the catalyst toward the epoxidation reactions. Thiscompound may be chosen from mineral or organic bases, mixtures of a saltand of its conjugate acid or base (known as “buffer mixtures”), salts,and mixtures thereof Examples of mineral bases are strong bases such asNaOH and KOH, or weak bases such as NH₄OH. Examples of organic bases areorganic molecules comprising one or more nitrogenous groups, forinstance an amine group (for example ethanolamine) or an amide group inwhich the nitrogen atom optionally bears at least one hydrogen atom (forexample urea), and nitriles (for example acetonitrile). An example of abuffer mixture that is very suitable is a mixture of ammonium chlorideand ammonia. Examples of salts are basic, acidic or neutral, organic orinorganic metal salts. It may also be an ammonium salt. Generally, themetal is chosen from alkali metals and alkaline-earth metals. The alkalimetals most often used are lithium, sodium, potassium and cesium. Sodiumis preferred. The alkaline-earth metals that may be used are mainlymagnesium, calcium, strontium and barium. The salts that may be used aremainly the halides, oxides, hydroxides, carbonates, sulfates, phosphatesand salts of organic acids, such as acetates. The halides are generallyfluorides, chlorides, bromides and iodides. A preference is shown forchlorides.

The amount of compound for increasing the selectivity of the catalystused in the process according to the invention is generally greater thanor equal to 10⁻⁶ mol per kg of reaction medium, advantageously greaterthan or equal to 10⁻⁵ mol/kg of reaction medium and preferably greaterthan or equal to 10⁻⁴ mol/kg of reaction medium. The amount is usuallyless than or equal to 2 mol/kg of reaction medium, in particular lessthan or equal to 1 mol/kg of reaction medium and more especially lessthan or equal to 0.5 mol/kg of reaction medium.

The compound for increasing the selectivity of the catalyst may beintroduced into the reactor via the peroxide compound feed, or via theorganic solvent feed, or separately. When the process is continuous, itis preferably introduced continuously.

Certain compounds capable of increasing the selectivity of the catalystinduce a decomposition of H₂O₂, which harms the viability of theprocess. In order to reduce this decomposition, it may prove to beadvantageous to introduce into the reaction medium a chelating agent asdescribed in patent U.S. Pat. No. 5,591,875.

Another essential characteristic of the invention lies in the fact ofhaving, in the liquid phase or in all of the liquid phases, a totalorganic solvent content of greater than or equal to 0.1 g/kg and lessthan or equal to 675 g/kg. This organic solvent content is generallygreater than or equal to 1 g/kg, in particular greater than or equal to10 g/kg and preferably greater than or equal to 50 g/kg. The organicsolvent content is usually less than or equal to 650 g/kg, moreespecially less than or equal to 600 g/kg and usually less than or equalto 550 g/kg.

In the process according to the invention, it is preferable for theliquid phase or all of the liquid phases to have a total content ofwater plus peroxide compound (preferably hydrogen peroxide) that isgreater than or equal to 100 g/kg, in particular greater than or equalto 125 g/kg, more particularly greater than or equal to 150 g/kg andpreferably greater than or equal to 200 g/kg. The total content of waterplus peroxide compound (preferably hydrogen peroxide) is usually lessthan or equal to 990 g/kg, more especially less than or equal to 950g/kg, or even less than or equal to 925 g/kg, values of less than orequal to 900 g/kg being the most common.

The oxirane that may be prepared by the process according to theinvention is an organic compound comprising a group corresponding to thegeneral formula:

The oxirane generally contains from 2 to 20 carbon atoms and preferablyfrom 3 to 10 carbon atoms. An oxirane that may be advantageouslyprepared by the process according to the invention is 1,2-epoxypropaneor 1,2-epoxy-3-chloropropane.

The olefins that are very suitable in the process according to theinvention generally contain from 2 to 20 carbon atoms and preferablyfrom 3 to 10 carbon atoms. Olefins containing from 2 to 4 carbon atomsare preferred, and in particular propylene or allyl chloride, in whichcase the oxirane produced is 1,2-epoxypropane or1,2-epoxy-3-chloropropane.

It may be advantageous to introduce the olefin into the reactor, inwhich the epoxidation reaction takes place, in diluted form in one ormore alkanes. For example, a fluid containing the olefin and also atleast 10% (in particular 20%, for example at least 30%) by volume of oneor more alkanes may be introduced into the epoxidation reactor. Forexample, in the case of propylene, said propylene may be mixed with atleast 10% by volume of propane when the recycled unconverted propyleneis introduced into the reactor. It may also be a source of propylenethat is not completely purified of propane.

The peroxide compounds that may be used in the process according to theinvention are organic and inorganic peroxide compounds containing one ormore peroxide (—OOH) functions that can release active oxygen and thatare capable of carrying out an epoxidation. Hydrogen peroxide andperoxide compounds that can produce hydrogen peroxide under theepoxidation reaction conditions are very suitable. Hydrogen peroxide ispreferred.

When hydrogen peroxide is used, it may be advantageous to use in theprocess according to the invention an aqueous hydrogen peroxide solutionin crude form, that is to say unpurified form. For example, a solutionobtained by simple extraction, with substantially pure water, of themixture derived from the oxidation of at least onealkylanthrahydroquinone may be used (process known as “autoxidation AOprocess”) without a subsequent washing and/or purification treatment.These crude hydrogen peroxide solutions generally contain from 0.001 to10 g/l of organic impurities expressed as TOC (Total Organic Carbon).They usually contain metal cations (such as alkali metals oralkaline-earth metals, for instance sodium) and anions (such asphosphates or nitrates) in contents of from 0.01 to 10 g/l.

The organic solvents that may be used in the process according to theinvention may be aromatic or aliphatic organic derivatives, theseorganic derivatives containing, for example, from 1 to 4 carbon atoms.They are preferably alcohols such as methanol or isopropanol. Methanolis preferred. Acetonitrile may also be used.

The catalysts used in the process according to the invention generallycontain a zeolite, that is to say a solid containing silica that has amicroporous crystalline structure. The zeolite is advantageously free ofaluminum. It preferably contains titanium.

The zeolite that may be used in the process according to the inventionmay have a crystalline structure of ZSM-5, ZSM-11 or MCM41 type or ofbeta zeolite type. Zeolites of ZSM-5 type are very suitable. Those withan infrared adsorption band at about 950-960 cm⁻¹ are preferred.

The zeolites that are particularly suitable are titanium silicates.Those corresponding to the formula xTiO₂(1−x)SiO₂ in which x is from0.0001 to 0.5 and preferably from 0.001 to 0.05 are highly efficient.Materials of this type, known as TS-1 and having a crystalline structureof ZSM-5 type, give particularly favorable results.

Advantageously, the catalyst has the form of spherical particlesobtained by any known method.

The catalyst particles generally have a mean diameter of greater than orequal to 0.01 mm and less than or equal to 5 mm, a specific surface areaof greater than or equal to 1 m²/g and less than or equal to 900 m²/g(determined according to the nitrogen adsorption method), an apparentdensity of between 0.1 and 1.0 g/ml, a pore volume of between 0.25 and2.5 ml/g and a pore diameter distribution with a maximum of between 15and 2000 Å.

According to one preferred variant of the present invention, the oxiraneis 1,2-epoxypropane (or 1,2-epoxy-3-chloropropane), the olefin ispropylene (or allyl chloride), the peroxide compound is hydrogenperoxide and the catalyst is titanium silicalite, preferably of TS-1type with a crystalline structure of ZSM-5 type.

The temperature at which the olefin reacts with the peroxide compound isgenerally greater than or equal to 0° C. and preferably greater than orequal to 35° C. It is advantageous to perform the reaction at atemperature of greater than or equal to 40° C. and preferably greaterthan or equal to 45° C. A temperature of greater than or equal to 50° C.is most particularly preferred. However, the reaction temperature isgenerally less than or equal to 120° C., often less than or equal to100° C. and preferably less than or equal to 80° C.

In the process according to the invention, when it is performedcontinuously, the peroxide compound is generally used in an amount of atleast 0.005 mol per hour and per gram of zeolite, in particular of atleast 0.01 mol per hour and per gram of zeolite. The amount of peroxidecompound is usually less than or equal to 5 mol per hour and per gram ofzeolite and in particular less than or equal to 3 mol per hour and pergram of zeolite. Preference is shown for an amount of peroxide compoundof greater than or equal to 0.03 mol per hour and per gram of zeoliteand less than or equal to 2 mol per hour and per gram of zeolite.

In the process according to the invention, the peroxide compound isadvantageously used in the form of an aqueous solution. In general, theaqueous solution contains at least 10% by weight of peroxide compoundand in particular at least 20% by weight. It usually contains a maximumof 70% by weight of peroxide compound and in particular 50% by weight.

Generally, the molar ratio between the amount of olefin used and theamount of peroxide compound used is greater than or equal to 0.1 andless than or equal to 100. Advantageously, this ratio is greater than orequal to 0.5 and less than or equal to 50. Preferably, this ratio isgreater than or equal to 1 and less than or equal to 25.

In the process according to the invention, it may moreover proveadvantageous to maintain the pH of the liquid phase during the reactionbetween the olefin and the peroxide compound at a value of at least 4.8and in particular of at least 5. The pH is advantageously less than orequal to 6.5 and in particular 6. Good results are obtained when the pHis from 4.8 to 6.5 and preferably from 5 to 6. The pH of the liquidphase during the epoxidation reaction may be controlled by adding a baseor a mixture of a salt and its conjugate acid or base. The base may bechosen from water-soluble bases. They may be strong bases. They may alsobe weak bases.

In one particular embodiment of the process according to the invention,the pressure during the reaction is adapted to the solubility of theolefin in the liquid phase constituting the reaction medium. Generally,this pressure is greater than or equal to atmospheric pressure (1 bar),preferably greater than or equal to 2 bar, or even greater than or equalto 5 bar. This pressure generally does not exceed 40 bar, or even 30bar, for practical reasons. A pressure of less than 20 bar gives goodresults.

In the process according to the present invention, the olefin may be fedinto the reactor in gaseous form, and its dissolution in the liquidphase then proceeds in situ in the reactor. Alternatively, andpreferably, the olefin is predissolved in at least one fraction of theliquid phase before it is fed into the reactor. In a particularlypreferred manner, the reactor is fed with a single flow of liquid inwhich the olefin has been predissolved under a pressure adapted to thedesired content in the reaction medium.

The reaction between the olefin and the peroxide compound may beperformed in continuous or batchwise mode. It is preferably performedcontinuously. In this case, the reactor is advantageously fed with asingle flow of liquid in which the olefin has been predissolved. Thepressure used to dissolve the olefin is preferably in the region of thatpresent in the reactor. An olefin content greater than or equal to 10g/kg, preferably greater than or equal to 40 g/kg, or even greater thanor equal to 75 g/kg, is thus generally obtained in the reactor feedflow. However, this content is generally less than or equal to 500 g/kg,preferably less than or equal to 400 g/kg, or even less than or equal to300 g/kg.

Advantageously, in the process according to the present invention, theoxirane produced is removed from the reaction medium by depressurization(in the case where the oxirane produced is gaseous at atmosphericpressure) and/or by stripping using a gaseous compound. Specifically, ithas been found that the oxirane reacts in the epoxidation reactionmedium with the water that accompanies the peroxide compound and/or theorganic solvent to form by-products, thereby reducing the selectivity ofthe epoxidation reaction. By introducing a gaseous compound into thereaction medium at a flow rate that is sufficient to strip out theoxirane produced and to remove it from the reaction medium at the sametime as the gaseous compound, and/or by sufficiently reducing thepressure of the reaction medium, the contact time between the oxiraneproduced and the epoxidation reaction medium is reduced. The formationof by-products is thus avoided and the epoxidation selectivity isincreased. Preferably, the oxirane formed is removed bydepressurization/stripping in a proportion of at least 50%, or even 75%.However, at least 1% generally remains in the liquid phase, or even atleast 5%. The gaseous compound that may be used in this particularembodiment of the process according to the invention may be any compoundthat is in gaseous form under the epoxidation conditions and that has nonegative impact on the epoxidation reaction. It may be chosen from inertgases such as nitrogen. It may also be the olefin when said olefin isgaseous and used in excess.

In the case of such a continuous process, at least some of the liquidphase leaving the reactor is advantageously recirculated. To this end, aloop reactor is preferably used, that is to say a reactor equipped witha device that is adequate for carrying out this recirculating.

Preferably, the reactor comprises a bed of the catalyst according to theinvention. This bed may be a fixed bed or a fluid bed. It isadvantageously a fluid bed.

In one preferred embodiment of the present invention, water isintroduced solely as diluent for the peroxide compound, that is to saythat the reactor is not fed with water per se, but only via the peroxidecompound that is in aqueous solution. This variant is particularlyadvantageous in the case of a continuous process in which at least someof the liquid phase is recycled.

In general, in order to maximize the production efficiency of theprocess, the amount of olefin is pushed to the maximum (for example bymaking it greater than 100 g/kg). Similarly, it is advantageous for theconcentration of the peroxide compound solution used to be high (forexample up to 70% by weight). Since the process is generally performedat a high degree of conversion and since a lot of water is consequentlyproduced in the reactor after the peroxide compound has been consumed,an additional supply of water to the reactor may be avoided if theprocess is performed continuously with recycling of at least some of theliquid phase.

An example of a process according to the present invention isrepresented diagrammatically in FIG. 1. A liquid flow called the“shuttle” is introduced into the bottom of a reactor (1) containing azeolite-based catalyst via a pipe (2). This flow comprises an olefin, aperoxide compound, water, formed oxirane, one or more organic solventsand one or more compounds capable of increasing the selectivity of thecatalyst toward the epoxidation reactions. The liquid flow circulates inthe reactor in the direction of the arrows. On leaving the reactor, thereaction medium is depressurized by means of a valve (3). Thisdepressurization is followed by the sparging of a gaseous compound usinga flow meter (4) in a stripping column (5). A gas mainly consisting ofthe produced oxirane, unconverted olefin, the gaseous compound used forthe stripping and traces of organic solvent, leaves the stripping column(5) via the pipe (6). The liquid phase leaving the top of the column ispartly recycled into the reactor via the pipe (7) and partly removed viathe overflow pipe (8). The peroxide compound is added to the recycledfraction via the pipe (9), and organic solvent is added via the pipe(10). The compound capable of increasing the selectivity of the catalystmay be added via the peroxide compound or via the organic solvent. Themixture thus obtained then passes into a saturator (12) via a pump (11).This saturator is fed with olefin under pressure via a flow meter (13),and at its outlet are collected, on the one hand, a gaseous phase ofundissolved olefin that leaves through the pipe (14) via adepressurization valve (15), and on the other hand, the shuttle that isfed into the reactor (1) via the pipe (2).

EXAMPLES

Two series of 4 tests were carried out, one (not in accordance with theinvention) in a medium with a high content of organic solvent (CH₃OH,860 g/kg), the other (in accordance with the invention) in a medium witha low content of organic solvent (CH₃OH, 530 g/kg). These 4 tests werecarried out according to the following scheme:

a first reference test, without addition of a compound capable ofincreasing the selectivity of aii epoxidation catalyst,

a second test with addition of NaCl so as to bring the Na concentrationin the reaction medium to a level of 55 ppm,

a third test with addition of sodium acetate (CH₃COONa) so as to bringthe Na concentration in the reaction medium to a level of 55 ppm,

a fourth test with addition of ethanolamine (NH₂CH₂CH₂OH) so as to bringits concentration in the reaction medium to 100 ppm.

For these tests, a plant according to FIG. 1 was used and propylene waschosen as olefin, H₂O₂ was chosen as peroxide compound and TS-1, in theform of beads consisting of 35% titanium silicalite dispersed in asilica matrix (65% by weight) and obtained by a process of sol-gel type,was chosen as catalyst. The oxirane produced is 1,2-epoxypropane orpropylene oxide (PO). The stripping gas was nitrogen.

Since Pe (propylene) is less soluble in a medium with a low methanolcontent, the pressure in the saturator was adjusted to keep the Peconcentration constant in the two series of measurements. The molar flowrate of H₂O₂ was also kept constant at 0.17 mol/h. The methanol flowrate and the flow rate of nitrogen used for the stripping were adjustedto maintain a constant residence time in the plant. The flow rate of theoverflow liquid was about 106 g/h. The shuttle circulation speed was 5l/h.

The conditions of these tests are given in Table 1 below.

TABLE 1 Series 1 Series 2 TS-1 used (g) 1.58 1.58 T° reactor (° C.) 5555 Conc. H₂O₂ solution used (% by weight) 39 10 Flow rate of H₂O₂solution (g/h) 15.2 59 H₂O₂ used (mol/h) 0.17 0.17 Pe (mol/kg) 0.24 0.24CH₃OH used (ml/h) 230 120 Saturator pressure (bar) 2.6 8 N₂ flow rate(1N/h) 50 45 Plant residence time (h) 4 4 Residence time on catalyst(min) 5.5 5.5The liquid phase fed into the reactor (after 6 h) was analyzed and thecomposition below given in Table 2 was found.

TABLE 2 Series 1 Series 2 H₂O + H₂O₂ (g/kg) 90 460 CH₃OH (g/kg) 860 530Pe(g/kg) 10 10 PO (g/kg) 5.5 6.5After a running time of 24 h, the results below given in Table 3 wereobtained.

TABLE 3 Degree of conversion PO/C3f selectivity (%) of the H₂O₂ (%) (1)(2) Series 1 Series 2 Series 1 Series 2 Without addition 76.3 85.2 83.479.0 +NaCl 51.0 87.3 97.2 95.8 +CH₃COONa 31.1 86.2 97.9 97.4+NH₂CH₂CH₂OH 46.3 88.7 98.4 98.5 (1) Calculation of the degree ofconversion The degree of conversion of the H₂O₂ is calculated from theH₂O₂ inlet and outlet flow rates. TC(%) = 100 × (H₂O₂ used in mol/h -unconverted H₂O₂ in mol/h)/H₂O₂ used in mol/h with uncoverted H₂O₂ =H₂O₂ conc. of the overflow liquid in mol/kg × overflow liquid flow ratein kg/h (2) Calculation of the PO/C₃f selectivity PO/C₃f sel. (%) = 100× PO_(formed)/Σ(PO + by-products)_(formed)

1. A continuous or batchwise process for manufacturing an oxirane byreaction between an olefin and a peroxide compound in a reactorcontaining a liquid phase, in the presence of water, one or more organicsolvents, a catalyst and one or more compounds for increasing theselectivity of the catalyst toward epoxidation reactions, wherein whenthe process is performed in batchwise mode, the liquid phase present inthe reactor when the reaction starts has a total organic solvent contentof at least 0.1 g/kg and of not more than 675 g/kg, and when the processis performed continuously, all of the liquid phases that are fedcontinuously into the reactor have a total organic solvent content of atleast 0.1 g/kg and of not more than 675 g/kg.
 2. The process accordingto claim 1, wherein the total organic solvent content in the liquidphase present in the reactor and all of the liquid phases that are fedcontinuously into the reactor is not more than 600 g/kg.
 3. The processaccording to claim 1, wherein the peroxide compound is hydrogen peroxideand the total content of water plus hydrogen peroxide in the liquidphase present in the reactor and all of the liquid phases that are fedcontinuously into the reactor is at least 100 g/kg.
 4. The processaccording to claim 3, wherein the total content of water plus hydrogenperoxide in the liquid phase present in the reactor and all of theliquid phases that are fed continuously into the reactor is at least 150g/kg.
 5. The process according to claim 1, wherein the compound forincreasing the selectivity of the catalyst is chosen from mineral ororganic bases, mixtures of a salt and of its conjugate acid or base,salts, and mixtures thereof.
 6. The process according to claim 1,wherein the organic solvent is methanol.
 7. The process according toclaim 1, wherein the oxirane is 1,2-epoxy-propane or1,2-epoxy-3-chloropropane, the olefin is propylene or allyl chloride,the peroxide compound is hydrogen peroxide and the catalyst is titaniumsilicalite of TS-1 type with a crystalline structure of ZSM-5 type. 8.The process according to claim 1, wherein the olefin reacts with theperoxide compound at a temperature of from 10 to 1200C and at a pressureof from 1 to 40 bar.
 9. The process according to claim 1, wherein theprocess is continuous, all of the liquid phases are fed into the reactoras a single flow in which the olefin has been dissolved, at least someof the liquid phase leaving the reactor is recirculated, and water isintroduced solely as diluent for the peroxide compound.
 10. The processaccording to claim 9, wherein the total olefin content in the liquidflow fed into the reactor is at least 10 g/kg, and the oxirane isremoved from the reaction medium by depressurization and/or strippingusing a gaseous compound.
 11. The process according to claim 1, whereinthe process is performed in batchwise mode.
 12. The process according toclaim 1, wherein the process is performed continuously.
 13. The processaccording to claim 1, v:herein the oxirane is 1,2-epoxy-propane.
 14. Theprocess according to claim 1, wherein the oxirane is1,2-epoxy-3-chloropropane.
 15. The process according to claim 2, whereinthe process is performed in batchwise mode.
 16. The process according toclaim 2, wherein the process is performed continuously.
 17. The processaccording to claim 7, wherein the process is performed in batchwisemode.
 18. The process according to claim 7, wherein the process isperformed continuously.